which LimeSurvey version do you use? LimeSurvey 1.92RC1 or 1.92RC2? We had a discussion at www.limesurvey.org/de/forum/development/...-in-validation-field and it came to the point whhere we discussed if this messages should be hidden. If I'm correct TMSWhite fixed/updated it in LimeSurvey 1.92RC3 (or a few build after this release candidate) so it might be a good idea to update your/install a new LimeSurvey installation.

In 1.92 RC4, we have eliminated the display of the regular expression validation message, since we figure very few people would understand it. Instead, if people want to guide users, they can put a readable tip in the Help message, or in the new em_validation_sq or em_validation_q advanced question options.

To add regular expression validation of short text or multiple short text, simply enter the regular expression in the "validation" field (one of the core fields, not one of the advanced question settings). This regular expression will be used to validate the short text input (or each of the multiple short text inputs, if that is the question type you use).

the preg field is question specific, so in the future, we could allow for sub-question-level validation - e.g. a different regex for each sub-question. Right now, that isn't supported. However, it would really only require a new GUI to enter sub-question-level validation (and relevance, since that is also often desired), plus minor changes to EM.